Mexico's electoral court set to confirm Pena Nieto victory

The problems are aggravated by weak legal provisions toprosecute alleged financial crimes, said Edgardo Buscaglia, anexpert on money laundering at Columbia University in New York.

"Electoral violations are obscene (but) there is noinstitutional framework to detect before or after the electionwhat is really going on," he said. "There is no way to find out,judicially speaking, where the money comes from."

The PRI was long dogged by accusations of vote-buying andcorruption during its decades-long grip on power.

In 2000, officials were accused of funneling over $100million from state oil firm Pemex to fund the PRI's unsuccessfulpresidential bid. Electoral authorities fined the PRI butprosecutors failed to convict officials linked to the crime.

Lopez Obrador's allies have been accused of using similartactics. In 2004, a close aide of Lopez Obrador was caught oncamera stuffing wads of cash into a suitcase.

Under current law, Lopez Obrador's charges of overspending are likely to only result in fines for the PRI, experts said.

Pena Nieto himself has sought to dispel doubts about hisprobity by pushing anti-corruption reform plans to the top ofhis agenda. He is promising to extend transparency laws to thestate and local level after he takes office.